In copending application Ser. No. 06/147,031, Grahame, there is described a number of fluid blends for certain capacitors defined as those capacitors having electrodes comprising paper strips which are metallized on both sides with a dielectric strip positioned between the electrodes. These capacitors, referred to as metallized paper capacitors were predominantly manufactured in a round roll, round casing form because certain parameters such as winding tension, space factor and roll integrity were deemed critical, and optimally obtainable only in the geometry of a round roll. Because of the criticality of the structure, great emphasis was placed on the kind of fluid to be used for impregnation because the characteristics of the fluid were required to be specifically correlated with the round structure.
In the noted copending application, it was discovered that such a capacitor could be greatly improved by the use of certain fluid blends of esters and hydrocarbons. Evidently the use of single chemical compounds and particularly blends of hydrocarbons and esters preserved the total optimum characteristics of the round roll construction while at the same time improving performance.
The prior art flattened or oval capacitor roll construction detracted from the integral rigid geometric round roll. The flattening process introduced wide variances in winding tensions and space factor and a general relaxation of stresses in the flattened areas. Fluid impregnants in these capacitors could not perform well because of the nonuniformity of the space factor, and limited swelling of the resin dielectric by the fluid left nonuniformly filled spaces in some parts of the roll. However, the flattened or oval roll construction is desirable for many reasons including its space saving considerations and its ability to thermally expand and contract more favorably.